Conventionally, a technique for producing an entangled nonwoven fabric by entangling constituent fibers with each other by jetting a high pressure fluid flow to a fabric web has been known as it is disclosed in for example Japanese Patent Application Laid-Open (JP-A) No. 51-133579 (patent document 1), JP-A No. 9-256254 (patent document 2), JP-A No. 2000-144564 (patent document 3), or the like. However, as the high pressure fluid disclosed in the patent documents 1 to 3, a high pressure liquid is used mainly. According to a production of an entangled nonwoven fabric by jetting a high pressure liquid flow, not only a liquid scattering prevention equipment is required due to a large liquid use amount and a purifying process equipment is required for the large amount of the liquid at a time of discharging the liquid after the process, but also a drying equipment for the obtained nonwoven fabric and a gigantic thermal energy consumed therefor are required. Moreover, noise based on a liquid jetting operation is rampant so as to deteriorate a work environment.
On the other hand, for example, although use of high pressure steam in stead of the high pressure liquid is mentioned in the above-mentioned patent document 1 and patent document 3, it is not for actively entangling the fibers or it is adopted without a recognition of a difference between the liquid flow and the steam flow. As a result, according to the patent documents 1 and 3, a jetting nozzle of the same structure is used without especially distinguishing the liquid flow and the steam flow, and thus a specific disclosure is not at all provided for the nozzle structure in consideration to a behavior peculiar to the jetted steam or a steam supply mechanism or discharging mechanism.
In order to solve problems at a time of producing the fiber entangled nonwoven fabric by the high pressure liquid flow, for example, WO 95/06769 pamphlet (patent document 4), JP-A No. 7-310267 (patent document 5), and the patent document 2 proposes active use of the steam as the high pressure fluid at the time of producing a nonwoven fabric by the high pressure fluid flow. In a case the steam is used, compared with the water jetting method, the water use amount can drastically be reduced as well as the discharging process equipment therefor can be miniaturized so that the noise generation can be reduced so as to improve the work environment. Additionally, the drying device can be eliminated or miniaturized for realizing energy saving. Furthermore, generation of a pattern at an entangled parts appearing on a nonwoven fabric surface peculiar to the fiber entangled nonwoven fabric by the liquid flow can be alleviated.
According to a production method for the nonwoven fabric of the above-mentioned patent document 4, an end product (nonwoven fabric) is produced by providing a fiber having a melting point lower than a temperature of the steam or superheated steam as an entirety or a part of a constituent fiber for the fiber web, producing a cloth (nonwoven fabric) preliminarily by entangling the web constituent fiber by a liquid flow, then jetting the steam or the superheated steam from a cloth surface toward a cloth inside so as to melt and fuse a low melting point fiber in the web constituent fiber. Moreover, a web entangling method disclosed in the above-mentioned patent document 5 is for entangling the web fiber with each other by using the steam as the high pressure fluid. According to a production method for the nonwoven fabric disclosed in the above-mentioned patent document 2, the nonwoven fabric is produced by jetting directly the steam to the fiber web instead of the conventional high pressure jetting water so as to function with fog like water generated by a temperature drop at a time for entangling the web constituent fiber.
According to an analysis of a content of the above-mentioned patent document 4, although use of high temperature steam is mentioned, various conditions peculiar to the fiber entanglement by the steam such as a steam pressure at the time of jetting and a nozzle hole size, a shape, or the like, are not mentioned. From this aspect, it is understood that the production of the nonwoven fabric by for example a high temperature superheated steam flow disclosed in the patent document 4 aims mainly at melting the fiber web constituent fiber made of a thermally fusible material by the steam heat instead of entangling the fiber by its steam flow. In general, as it is disclosed for example in the above-mentioned patent document 3, the fiber entangled nonwoven fabric produced by jetting a high pressure water flow has a hitting trace or an open hole trace by the jetting fluid.
According to the production method for a nonwoven fabric of the above-mentioned patent document 4, fiber entangling by the jet water flow is executed as a pre-process for jetting the steam to the fiber web. Therefore, it is considered that naturally the hitting trace and open hole trace remain on the cloth with the fiber entangling by the jet water flow so that the high temperature steam jetted thereto passes mainly through the hitting trance and open hole trace without penetrating through in a thickness direction in a cloth entire surface. Of course, another low melting point fibers present on the web surface without formation of the hitting trace or open hole trace are molten at the same time. It is recognized from a fact that parts with the fibers fused with each other are present in a region without formation of the hitting trace or open hole trace in FIGS. 4 to 5 in the patent document 4. As a result, the nonwoven fabric shown in the figures is not different from the conventional nonwoven fabric produced by point bonding in terms of flexibility, and there are hardened parts by the thermally fusible material particularly on the surface.
Moreover, although a structure of an embodiment of a steam jetting nozzle is shown in a figure of the above-mentioned patent document 5, the structure, a size, a use embodiment, or the like of the jetting nozzle is not at all mentioned specifically.
On the other hand, although the above-mentioned patent document 2 discloses a specific structure of a steam jetting nozzle, how the steam is sent into the jetting nozzle and what kind of conditions are required to jet the high pressure steam evenly and continuously from the nozzle are not disclosed specifically. As the steam used for the jetting operation, in general, industrial water with a soft water process and a slight amount of an additive added is used. Furthermore, since it passes through various kinds of tubes, or the like, extremely fine foreign substances can be mixed in the steam so that the jetting nozzle holes can easily be choked. Or since a part of the steam introduced into the nozzle is condensed so as to be drainage and pooled in a vicinity of the nozzle hole, the nozzle hole can easily be choked and thus the steam can easily be jetted intermittently instead of jetted continuously. Furthermore, although the nozzle structure disclosed in the patent document 2 can be adopted preferably for a fluid flow jetting nozzle, a number of parts is too large so that it is too complicated for a steam jetting nozzle.
The present invention has been achieved for solving the above-mentioned problems, and an object thereof is to provide a pressurized steam jetting nozzle having a simple structure, capable of jetting pressurized steam evenly and continuously, obtaining a predetermined strength by certainly entangling a part or substantially the entirety of the constituent fibers of a fiber web, ensuring a surface flexibility of the nonwoven fabric to be obtained, and improving an internal embodiment thereof, an efficient production method for a nonwoven fabric capable of certainly entangling the constituent fibers of a fiber web by jetting pressurized steam using the nozzle, and a continuous production apparatus for a high quality fiber entangled nonwoven fabric by steam using the nozzle.